1. Field of the Invention
The present invention relates to an apparatus for reading a color image and, more particularly, to a color image reading apparatus for reading an image of a color negative film.
2. Related Art of the Invention
The applicant of the present invention has already proposed an apparatus in which an image recorded on a microfilm is photoelectrically read using an image sensor such as a CCD or the like and electrical image signals are output in U.S. Pat. applications Ser. Nos. 786,638 (filed on Oct. 11, 1985), 854,569 (filed on Apr. 22, 1986), 878,790 (filed on June 26, 1986), 924,433 (filed on Oct. 29, 1986), and the like.
For example, when the image recorded on a microfilm is read, since it is generally a black and white image, by discriminating a transmission light quantity of the film, the image can be relatively easily read.
On the other hand, the present applicant has also already proposed an apparatus for photoelectrically reading an image on a color film in U.S. Pat. continuation application Ser. No. 057,657 (filed on June 8, 1987) and U.S. Pat. application Ser. Nos. 013,119 (filed on Feb. 10, 1987), and 013,731 (filed on Feb. 11, 1987). However, when considering the case where the image on, e.g., a color negative film is read, the transmission factor of the color negative film largely varies in dependence on the exposure conditions upon photographing and even if the CCD output is directly A/D converted, the proper R, G, and B signals cannot be obtained. On the other hand, by properly processing the R, G, and B signals after the A/D conversion in accordance with the state of the film, they can be converted into the proper R, G, and B signals. However, in this case, the number of effective bits of the data decreases, causing the quality of the readout image data to be deteriorated.